A common lamp that has achieved great commercial success is the linear fluorescent tube lamp which is an elongated lamp with an isotropic light emission along the length of the lamp. Fluorescent tube lamps are commonly used in office, commercial, industrial and domestic applications and are available in standard sizes such as T5, T8, and T12 lamps.
A lighting arrangement that is commonly used in office and commercial applications is a ceiling-recess or troffer that is mounted within a modular suspended (dropped) ceiling. Other, linear lighting arrangements include suspended linear arrangements that can be direct only (downward light emitting) or direct/indirect (lighting both the workspace in a downward direction and the ceiling in an upward direction for indirect lighting. Surface mount linear fixtures, often called wrap-around lights or wrap lights, are used in office, industrial and domestic spaces. These are typically mounted directly to the surface of the ceiling or a wall. Task lighting and under-cabinet fixtures also commonly use linear lamps as the light source.
FIG. 1 shows an example of a traditional troffer 10 that is used to house fluorescent tube lamps in a modular suspended (dropped) ceiling. The interior of the troffer body 12 includes lamp holders (connectors) on both lateral ends of the arrangement to receive linear fluorescent tubes 14. To achieve desired lighting performance, most troffers are configured to receive several fluorescent tubes, since a single conventional tube by itself cannot usually generate enough light for typical applications. To maximize light emission, the interior surface of the troffer body 12 is light reflective. The troffer can include a removable panel 16 to allow for insertion and replacement of the fluorescent tubes 14. In addition, the panel 16 also provides a location to include a diffuser within the lighting arrangement to improve the uniformity of emission of the arrangement and to reduce glare from the fluorescent tubes.
While traditional fluorescent-tube-based troffers, suspended linear, wrap-around lights and under-cabinet lighting arrangements are very common and exist in almost every commercial and office building, there are disadvantages with such lighting configurations; namely, their non-uniform emission characteristics and the appearance of glare from the fluorescent tubes.
In recent years, white light emitting LEDs (“white LEDs”) have become increasingly popular and are now more commonly used to replace conventional fluorescent, compact fluorescent and incandescent light sources. White LEDs generally include one or more photoluminescence materials (typically inorganic phosphor materials), which absorb a portion of the radiation emitted by the LED and re-emit light of a different color (wavelength). The phosphor material may be provided as a layer on, or incorporated within a wavelength converting component that is located remotely from the LED. The latter arrangements are commonly referred to as “remote phosphor” arrangements. As is known, LED-based linear lamps can comprise a linear array of discrete white LEDs or a remote phosphor arrangement comprising a linear array of blue LEDs with a linear remote wavelength converting component overlaying the LEDs. While such LED-based linear lamps provide many benefits over traditional fluorescent lamps, such as improved efficiency and longer life expectancy, they typically possess a substantially Lambertian emission characteristic which can result in pronounced hot spots associated with each LED-based linear lamp. Moreover, in the case of lamps comprising a linear array of discrete white LEDs, these can exhibit pronounced hot spots associated with each of the discrete white LEDs. Such emission characteristics and hot spots are particularly undesirable in troffer applications.
The present invention arose in an endeavor to provide LED-based linear lamps that in troffer-type applications, at least in part, improve the uniformity of emission and reduce the appearance of hot spots.